In vehicles, such as automobile, in recent years, in order to stabilize a vehicle's running motion, a variety of behavior controls, motion controls or running controls have been more often executed. In these controls, a control of a braking-driving force of each wheel or a steering angle of a vehicle is executed using a model of a vehicle body motion or tires, so that the motion condition (yawing, rolling etc.) of the vehicle can be stabilized. For instance, in the controls of ABS (Anti-lock Braking System), TRC (Traction Control), etc., the magnitudes of the braking-driving forces applied to the respective wheels are controlled in order to adjust the slip ratios of the respective wheels so that the tire force of each wheel does not exceed beyond a friction circle. Further, in VSC (Vehicle Stability Control), in order to stabilize a vehicle motion in the yaw direction, a braking-driving force difference between right and left wheels or a steering angle of a vehicle is controlled, and thereby the yaw moment control around the centroid of the vehicle is attained.
As understood by one skilled in the art, in the execution of a vehicle's behavior, motion or running control as described above, characteristic values which vary depending on the amount and arrangement of loaded objects (loaded condition) on a vehicle, such as a vehicle weight, a stability factor, the distances from the vehicle's centroid to the front and rear wheel axles, wheel axle loads on the respective wheels, cornering powers of the respective wheels, etc., are often required as parameters for those controls. In a case of a typical private vehicle, since the variations in the number of riding persons or the amount of loaded objects in a vehicle are small, those parameters are approximately given as constant values. However, in a case of a vehicle of medium size to large size, e.g. a bus, a truck, etc., in which the variations in the amount and positions of loaded objects in a vehicle are large, it is preferable that the parameters which can vary depending on the amount of loaded objects on a vehicle are detectable during the use or running of the vehicle and available in the behavioral, motional or running controls in order to accomplish the more precise executions of the controls. Thus, in the prior art, it has been proposed to estimate, among the parameters which vary depending on the loaded condition of a vehicle, a vehicle weight from a relation between a driving force and acceleration or a relation between a braking force and deceleration during the running of a vehicle (Patent document 1). Moreover, it is known that a stability factor can be determined from detected values, such as a steering angle, a yaw rate and a vehicle speed of a running vehicle (Patent documents 2 and 3). Furthermore, in Patent document 4, there is proposed a device which directly detects each wheel axle load by means of a load sensor; estimates a vehicle weight and a longitudinal position of a vehicle centroid from the detected values; and uses the estimated values for a behavior control of a vehicle.    Patent document 1: Japanese patent Laid-Open publication 2002-333365    Patent document 2: Japanese patent Laid-Open publication 2004-26073    Patent document 3: Japanese patent Laid-Open publication H11-94711    Patent document 4: Japanese patent Laid-Open publication 2005-199882